1. Field of Technology
Embodiments disclosed herein relate generally to a light emitting lamp and more specifically a light emitting lamp that adaptively compensates for effects of cat-ear dimmers on conduction angle measurement.
2. Description of the Related Arts
Dimmer switches are devices used to control the brightness of light bulbs. One type of dimmer switch is a phase cut dimmer switch, also known as TRIAC dimmers. A phase cut dimmer switch reduces the amount of power delivered to a light bulb by receiving an AC voltage waveform and cutting off a portion of the AC voltage waveform. Some phase cut dimmers known as “cat-ear” dimmers use cat-ear power supplies to power the dimmer. These power supplies have an energy storage capacitor which provides power to the dimmer when the AC input is cut off.
FIG. 1 illustrates the voltage waveform 10 output by a cat-ear dimmer after it has been passed through a full wave rectifier. Each cycle of the voltage waveform 10 includes a phase cut 13 that is set by the dimmer switch to cut off the AC input voltage and reduce the power delivered to a light bulb. The phase cut creates dimming pulses 11. The energy storage capacitor of the cat-ear power supply charges through the light bulb around the zero-crossings of the AC source voltage. Some cat-ear dimmers assume worst case conditions and fix the charging time. Other cat-ear dimmers employ an additional circuit to monitor the energy storage capacitor voltage and increase or decrease the charging time as needed. This charging behavior creates additional pulses 12 in the output voltage waveform 100 that have the appearance of cat-ears.
Cat-ear dimmers have conventionally been used in conjunction with incandescent light bulbs. However, interfacing cat-ear dimmers with newer lighting technologies, such as LED-based lamps, represents a significant design challenge. When operating from a phase cut waveform, a dimmable LED controller may attempt to use the width of the dimmer pulse 11 as a proxy for the dimming level of the dimmer switch. However, the presence of the cat-ear pulse 12 makes it difficult to correctly measure the size of the dimmer pulse 11. The cat-ear pulse 12 can change from cycle to cycle. This results in instabilities in the measurements and causes the LED lamp to flicker. Additionally, cat-ear dimmers are only one of the many different dimmers that can be interfaced with a LED-based lamp. LED controllers that are specifically designed to work with cat-ear dimmers can result in sub-optimal performance when used with other types of dimmers.